A light emitting device includes a P-N junction diode having a characteristic of converting electrical energy into light energy. The light emitting device may be fabricated with compound semiconductors belonging to group III and V on the periodic table. The LED can produce various colors by adjusting the compositional ratio of the compound semiconductors.
When forward voltage is applied to the light emitting device, electrons of an N layer are combined with holes of a P layer, so that energy corresponding to an energy bandgap between a conduction band and a valance band may be generated. In the case of the light emitting device, the energy is generated in the form of light.
For example, a nitride semiconductor represents higher thermal stability and wide bandgap energy so that the nitride semiconductor has been spotlighted in the field of optical devices and high-power electronic devices. Specifically, blue light emitting devices, green light emitting devices, ultraviolet (UV) light emitting devices, and the like using nitride semiconductors are commercialized and widely used.
According to the light emitting device of the related art, an active layer serving as a light emitting layer is formed by repeatedly laminating a quantum well having a lower energy bandgap and a quantum barrier having a higher energy bandgap. In the quantum well, electrons injected through an N type semiconductor layer meet and are combined with holes injected through a P type semiconductor layer, thereby emitting light.
Meanwhile, according to the related art, a light emitting device has a droop problem in which light emission efficiency is lowered as the quantity of applied current is increased. This is because the efficiency of carrier (holes or electrons) injection into a light emitting layer is not uniform. In order to solve the above problem, there is required the development of a technique of substantially participating most quantum wells of the light emitting layer in light emission.
Recently, an ultraviolet light emitting device (UV LED) has been spotlighted in the use for sterilizing, purifying, or the like, or the use for exposure machine, curing machine, or the like. There is required a technique of increasing light emission efficiency of the UV LED by taking into consideration that the UV LED has a lower composition of indium (In) in a quantum well as compared to that of a light emitting device in a visible light region such as a blue light emitting device.